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Thursday, August 14, 2008

Virtual hand gets under the skin

These new amazingly realistic animations of the human hand go way beyond the demands of Hollywood (see video, right). They are detailed enough to shed light on the mystery of how the tendons and muscles of the human hand interact when we move, and should help surgeons reconstruct damaged hands more effectively.

Computer animators are adept at making characters that move realistically, largely thanks to advances in motion capture technology that records the way people move.

But even the best motion capture only records the movement of the body's surface. That's fine for a movie, but surgeons are less superficial. They are interested in the movement of muscles and tendons beneath the skin.

Now hand animations that go below the surface (see video, right), have been made, by Shinjiro Sueda, Andrew Kaufman and Dinesh Pai at the University of British Columbia in Vancouver, Canada.

Moving muscle

They used anatomical data from medical images to model the 17 bones and 54 tendons and muscles of the hand and forearm.

The team's software can coordinate the contraction and relaxation of muscles, and the way forces are transmitted by tendons to produce any desired hand gesture.

"Motion capture is data driven – you just capture the data and play it back," says Sueda. "Our approach is a simulation in which the starting point is the physics of muscle and tendon movement."

Sueda's team also clothed their virtual muscles and tendons in a layer of skin. Just like real skin its shape depends on the anatomy beneath it.

Helping hand

"The parameters to control the deformation of the skin aren't biomechanical – it's just cosmetic," says Sueda. But because the underlying controlled muscles and tendons are accurately placed, the result is a hand animation that is highly realistic.

When Sueda's team took screen grabs of their animated hands and compared them to photographs of real hands in the same position, the two sets of images match closely.

The model should be a boon to surgeons, says Sueda. "The network of muscles and tendons in the hand is very complicated," he adds. "Even now people don't know how it actually works in detail."

Although the anatomy of the hand was worked out long ago from dissections, the interplay of all the components when in motion has largely remained a mystery. For this reason, the results of hand surgery can be unpredictable.

Adding realism

When a tendon is damaged, the muscle it's attached to no longer functions properly. Surgeons try to restore movement by taking a nearby tendon and re-routing it along the path of the damaged one. But predicting the results of that is difficult.

"Using our technique, you can show what effect rerouting a tendon would have on the hand before you actually do the surgery," says Sueda.

The new technology has also been built as a plug-in for existing graphics software to allow animators to quickly and easily add more realism to their hand animations.

The new hand animation models will be presented at the SIGGRAPH computer graphics conference in Los Angeles on 15 August 2008.